As background, according to Ullman's Encyclopedia of Industrial Chemistry, 12th edition (2012), MTBE was studied extensively in the US during World War II as a high-octane fuel component but was not commercially manufactured until the mid-1970s. With the reduction in the lead content of gasolines at that time, demand for high octane additives increased. Further changes in the composition of gasolines increased demand for MTBE into the late 1990s, but the discovery in subsequent years of MTBE in some groundwater (by virtue of leaking underground storage tanks) has led to a curtailment of MTBE usage in the United States. Still, in Europe as well as in developing parts of the world, MTBE and ETBE remain widely used, commercially important fuel additives.
Conventionally, MTBE has been made in petroleum processing, in integrated processes for the production from a mixed C4 stream from petroleum crackers (after removal of multiply unsaturated hydrocarbons such as butadiene) of isobutene as used in making butyl rubber, polyisobutylene, isobutene oligomers and t-butyl aromatics, of tert-butanol (TBA) and MTBE in desired proportions. The art contains a number of examples of such integrated processes for making non-biobased, conventional MTBE, see, for example, U.S. Pat. No. 4,118,425 to Herbstman, U.S. Pat. No. 4,329,516 to Al-Muddarris, U.S. Pat. No. 4,423,251 to Pujado et al., U.S. Pat. No. 4,981,491 to Harandi et al., and U.S. Pat. No. 5,254,764 to Miracca et al., as well as Ullmann's Encyclopedia of Industrial Chemistry, 11th ed., “Methyl Tert-Butyl Ether”, pp 119-130, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim (2012). The art also contains an example of a more recent integrated process for making isobutene, in part by the dissociation of MTBE formed initially to facilitate the separation of isobutene from the mixed C4 stream, see US 2012/0142985 to Winterberg et al. ETBE for its part has been made in a like manner as MTBE, through using ethanol rather than methanol in the etherification step of such processes.
One of the obvious limitations of current MTBE and ETBE production is the dependence of the known processes for making MTBE and ETBE on petroleum resources and refining for supplying the isobutene to be etherified. In response to recent regulatory and legislative initiatives seeking to encourage the development and commercialization of renewable fuels and renewable source-based fuel additives, an MTBE product (“Bio-MTBE”) was launched in October 2012 by Evonik Industries AG that utilizes fossil fuel-derived isobutene with a biobased methanol made from glycerol, ostensibly by the catalytic reforming process described in WO 2010/104467 to Duan et al. (“Duan et al”, hereby incorporated by reference). Because glycerol is produced as a co-product of the biodiesel manufacturing process from triglycerides from oilseed crushing, the biobased methanol used by Evonik is said to be considered a waste product under the European Union Renewable Energy Directive, providing added value under the regulatory scheme for meeting EU specifications for biofuel use and CO2 reduction. Ethanol for ETBE, of course, has long been made from grains, yet in regard to Evonik's Bio-MTBE and equally in regard to ETBE by virtue of the isobutene's being derived from petroleum processing there remains an unmet need for wholly biobased MTBE and ETBE fuel additives. The commonly-assigned '433 and '312 applications provide means by which a biobased isobutene may be viably produced, for being combined according to the present invention with a biobased methanol to provide a desired wholly biobased MTBE, or with a biobased ethanol to provide a desired wholly biobased ETBE.